1. Field of the Invention
This invention relates to greases, and more particularly, to an overbased calcium sulfonate grease having improved physical properties.
2. Description of the Prior Art
Overbased greases are well known in the art, and are characterized by a metal content in excess of that which would be present according to the stoichiometry of the metal and the particular organic compound reacted with the metal, for example, a carboxylic or sulfonic acid. Various processes are disclosed in the prior art which are useful for making a product containing more than the stoichiometic amount of metal. Following these procedures, the sulfonic acid or an alkali or alkaline earth metal salt thereof can be reacted with a metal base and the product will contain an amount of metal in excess of that necessary to neutralize the acid. The actual stoichiometic excess of metal can vary considerably, for example, from about 0.01 equivalent to about 30 or more equivalents, depending on the reactions, process conditions, and the like.
Prior art greases and lubricants are disclosed, for example, in the following U.S. Pat. Nos.: 2,977,301; 2,978,410; 3,186,944; 3,242,079; 3,376,222; 3,492,231; 3,907,691; 3,929,650; 4,376,060; 4,560,489; 4,597,880; and 4,824,584.
U.S. Pat. No. 4,560,489 discloses greases comprising a combination of (1) a highly overbased calcium sulfonate of a high molecular weight oil-soluble sulfonic acid, dissolved in an oil, containing extremely finely divided calcium carbonate; and (2) a product formed by the reaction of boric acid with a calcium compound such as calcium hydroxide or calcium oxide; and (3) a product formed from calcium hydroxide/calcium oxide and a soap-forming aliphatic monocarboxylic or fatty acid.
In making overbased greases, conversion agents are used to convert the Newtonian homogeneous, single-phase overbased materials into non-Newtonian colloidal disperse systems. U.S. Pat. No. 3,492,231 discloses the use of phosphorous acids as conversion agents in forming colloidal disperse systems.